1.1. To be able to answer the question To be able to answer the question “What is “What is Damping?”Damping?”

Book Reference : Pages 45-46Book Reference : Pages 45-46

What equipment do cars or bikes tend to have What equipment do cars or bikes tend to have to iron out the bumps in the road?to iron out the bumps in the road?

What do we observe in the “real-world”What do we observe in the “real-world”

How would a pendulum continue to swing in How would a pendulum continue to swing in an an “ideal physics world” “ideal physics world” with no friction & in a with no friction & in a vacuumvacuum

If the car suspension consisted only of If the car suspension consisted only of springs, what would happen to the motion springs, what would happen to the motion of the car for sometime after hitting a bump of the car for sometime after hitting a bump in the road?in the road?

Most vehicles use springs or similar to iron out Most vehicles use springs or similar to iron out the lumps and bumpsthe lumps and bumps

With only springs the vehicle will continue to With only springs the vehicle will continue to bounce (oscillate up and down) for some time bounce (oscillate up and down) for some time after hitting the bump and the passengers after hitting the bump and the passengers would feel sea sick. Think SHM!would feel sea sick. Think SHM!

Pendulum would keep going with full amplitude Pendulum would keep going with full amplitude for everfor ever

Friction and air resistance reduce the Friction and air resistance reduce the amplitude until eventually the pendulum stopsamplitude until eventually the pendulum stops

Shock absorbers Shock absorbers (dampers)(dampers)

Shock absorbers Shock absorbers (dampers)(dampers)

http://www.acoustics.salford.ac.uk/feschools/waves/shm4.htm

In the “real-world” a system in SHM such as a In the “real-world” a system in SHM such as a pendulum or a mass on a spring will eventually pendulum or a mass on a spring will eventually come to rest due to “losing energy”, actually come to rest due to “losing energy”, actually doing work against friction and air resistance!doing work against friction and air resistance!

What will the ride in the car be like whenWhat will the ride in the car be like when

1.1. The damping is not strong enoughThe damping is not strong enough

2.2. The damping is too strongThe damping is too strong

3.3. The damping is just rightThe damping is just right

No bears, kitchen furniture, porridge or small girls with golden No bears, kitchen furniture, porridge or small girls with golden hair were harmed in the making of this lesson hair were harmed in the making of this lesson

[VPL Damping][VPL Damping]

1.1. Light damping (under damping)Light damping (under damping)

2.2. Heavy damping (over damping)Heavy damping (over damping)

3.3. Critical dampingCritical damping

1.1. Light damping (under damping) Light damping (under damping) The The oscillation slowly dies away (exponential oscillation slowly dies away (exponential decay). decay).

2.2. Heavy damping (over damping) Heavy damping (over damping) The The damping is so strong that the displaced damping is so strong that the displaced object takes a long time to return to the object takes a long time to return to the equilibrium position and does not oscillateequilibrium position and does not oscillate

3.3. Critical damping Critical damping : just enough to stop the : just enough to stop the oscillation as quickly as possible often about oscillation as quickly as possible often about T/4 with little or no overshootT/4 with little or no overshoot

What caused this?What caused this?How could it be avoided?How could it be avoided?

Caravan Stabiliser :

Friction is introduced into the tow mechanism to damp both sideways and up and down motion

1) State is damping is light, critical or heavy in these cases:

A child on a swing, displaced and released

Oil in a U shaped tube displaced from equilibrium and released

2) What would happen if the oil in a damper (shock absorber) was replaced with very viscous (thick) oil?

1)1) A family car has an unloaded mass of 1000kg. The A family car has an unloaded mass of 1000kg. The mass is supported equally by 4 springs. When fully mass is supported equally by 4 springs. When fully loaded the total mass increases to 1250kg causing loaded the total mass increases to 1250kg causing the springs to compress by a further 2cm. When the springs to compress by a further 2cm. When the car hits a bump in the road it bounces. Find the car hits a bump in the road it bounces. Find the period of these oscillations.the period of these oscillations.

State assumptionsState assumptions

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